The present invention relates to the medical diagnostic imaging arts. It finds particular application in conjunction with a method and apparatus for reducing, suppressing, and/or eliminating noise and/or other image artifacts that are present in a diagnostic image that is generated by a flat panel image receptor of a diagnostic imaging system, and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with other types of imaging systems and applications where reducing noise and other image artifacts is desired.
The sensitivity of x-ray image detector devices, including flat panel image sensors or receptors, is limited by noise, i.e., random signal fluctuations that compete with data or other information that represents or otherwise defines a captured image. One type of noise that is characteristic of some flat panel image receptors, such as amorphous Silicon-based, flat panel image receptors, is line-correlated noise. Line-correlated noise can be defined as random fluctuations that affect a whole raster line of a video frame in a manner that causes all the picture elements (xe2x80x9cpixelsxe2x80x9d) of a raster line to commonly deviate from their actual captured image values.
The manifestation of line correlated-noise in a video image displayed on a video monitor is stripes that fluctuate in intensity across the width of the image. This is an undesirable effect that is highly distracting to medical personnel, such as physicians, when using a diagnostic imaging system, such as a fluoroscopic, radiographic, computed tomographic (CT), magnetic resonance (MR) imaging system, nuclear camera, etc., to perform interventional procedures.
There are known image processing techniques, generally referred to as blacklevel clamping or line noise clamping, for reducing the amount of line-correlated noise generated in image receptors. These techniques rely on one or more clamp or reference zones formed from corresponding strips of radiation impervious material such as lead. The clamp or reference zones are positioned along either one or both vertical side edges of an image receptor active area (i.e. perpendicular to the image raster lines) in front of corresponding radiation sensors. The clamp or reference zones effectively black-out or prevent the corresponding radiation sensors from receiving or capturing any x-ray radiation generated by an x-ray source. Thus, the radiation sensors are prevented from generating image information, and should give a zero output, but for noise.
The blacked-out reference zones are each a predetermined number of pixels wide. The only output signals or information received from the pixels within the blacked-out reference zones is random noise and line-correlated noisexe2x80x94the same line noise that affects the pixels in the exposed or active region of the image receptor.
Line noise cancellation involves determining the average output value of the reference pixels within the blacked-out zones for each raster line of each video frame to average out the random noise fluctuations of each reference pixel, and to yield the error introduced in that particular raster line by line noise alone. The resulting error value is then uniformly subtracted from each of the active area pixels in the corresponding raster line prior to being displayed on a video monitor.
The known blacklevel or line noise clamping techniques are hardware dependent. That is, the known clamping techniques require modifications/enhancements to an active area of the associated flat panel image receptor (e.g. providing lead strips on one or both vertical edges of the active area associated with a flat panel image detector). Although the lead strip technique works well for smaller detectors, it is not readily adapted to large detectors.
Accordingly, it is considered desirable to develop a new and improved method and apparatus for reducing noise artifacts in a diagnostic image, which method is hardware-independent (i.e. not a detector-related accessory), that meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.
In accordance with one aspect of the present invention, a method for generating corrected diagnostic image data is disclosed. The method includes a) acquiring uncorrected diagnostic image data from x-rays generated by an x-ray source; b) filtering the uncorrected diagnostic image data to generate noise image data; c) determining statistical data from a first subset of the noise image data; and d) correcting a second subset of the uncorrected image data based on the statistical data, the second subset of the uncorrected image data corresponding to the first subset of the noise image data.
In accordance with another aspect of the present invention, a medical diagnostic imaging apparatus is disclosed. The apparatus includes a source for generating x-rays, an image receptor for receiving the x-rays and generating image data, and an image processing subsystem for generating corrected image data from the image data acquired by the image receptor. The image processing subsystem includes a processor programmed to a) high-pass filter the image data acquired by the image receptor to generate high-pass filtered image data; b) select a region of interest from a plurality of regions of interest within the high-pass filtered image data, the region of interest comprising a plurality of first raster line segments; c) determine an integration value for each of the plurality of raster line segments; d) determine an average integration value for the region of interest; e) determine an error value for a selected one of the plurality of first raster line segments, the error value based on the integration value for the selected one of the plurality of first raster line segments and on the average integration value; and f) determine a noise-corrected pixel value for a pixel associated with a second raster line segment associated with the image data acquired by the image receptor, the second raster line segment corresponding to the selected one of the plurality of first raster line segments associated with the high-pass filtered image data.
In accordance with yet another aspect of the present invention, an apparatus for generating corrected diagnostic image data is disclosed. The apparatus includes a mechanism for acquiring uncorrected diagnostic image data from x-rays generated by an x-ray source; a mechanism for filtering the uncorrected diagnostic image data to generate noise image data; a mechanism for determining statistical data from a first subset of the noise image data; and a mechanism for correcting a second subset of the uncorrected image data based on the statistical data, the second subset of the uncorrected image data corresponding to the first subset of the noise image data.
One advantage of the present invention is the provision of a method and apparatus that reduces noise artifacts in a diagnostic image by extracting line fluctuations (i.e. noise) directly from image data generated from an x-ray detector.
Another advantage of the present invention is the provision of a method and apparatus that reduces noise artifacts in a diagnostic image using high pass filtering and data fitting techniques to extract line noise fluctuations.
Yet another advantage of the present invention is the use of a method and apparatus that reduces noise artifacts in selected regions of interest of a diagnostic image.
Still another advantage of the present invention is the use of a method and apparatus that reduces noise artifacts in a diagnostic image by providing a mechanism that optimizes the filtering of line noise from diagnostic image data.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.